Electrical distribution and control system



Aug. l2, 1969 F. KOPPELMANN ELECTRICAL DISTRIBUTION AND CONTROL SYSTEMFiled Jan. 1967 2 Sheets-Sheetl 1 ug. l2, 196g F. KOPPELMANN ELECTRICALDISTRIBUTION AND CONTROL SYSTEM Filed aan. e, 196? 2 Sheets-Sheet 2 SEG*tbtmwmm AJ., .W

AHM-hws Floris Koppelmcmh US. Cl. S18-107 9 Claims ABSTRACT F THEDISCLOSURE An A.C./D.C. electrical distribution and control system inwhich a regulated D.C. output voltage is derived from A.C. mains bymeans of a rectifier and a wound rotor induction motor connected inparallel between the A.C. mains and D.C. mains. The output of the woundrotor induction motor is rectified by a second rectifier and applied tothe D.C. mains in a controlled manner so that the average D.C. powersupplied by the motor is approximately equal to the load power drawnfrom the D.C. mains. A switchable ballast resistor is coupled across theD.C. mains to dissipate excess D.C. power. The ballast resistor isautomatically switched into the circuit when the D.C. Voltage exceeds apredetermined value.

Cross reference to related applications This application is acontinuation-in-part of copending application Ser. No. 414,738, nowabandoned, filed Nov. 30, 1964.

Background of the invention At the beginning of the development of theelectromotive art, electric motors were first energized by directcurrent mains. After the invention of alternating current motors,however, existing direct current mains were progressively replaced byalternating current mains, but now there has been a reversal in thistrend. Alternating current motors whose rotational speed is to becontrolled once more require direct current mains, the latter preferablybeing used in conjunction with an alternating current main. This isparticularly true where the power supply is to be used to supply aplurality of medium horsepower motors whose rotational speeds are to becontrolled independently of each other.

The above-noted increase in the use of D C. mains is principally due tothe increasing use of thyristors, i.e., solid state gatable rectifiers,as motor speed control devices which, in turn, require controlled D.C.mains.

It is, therefore, the primary object of the present invention to providean electrical distribution system in which both alternating and directcurrent mains are used for supplying electric energy to motors whosespeeds are to be regulated independently of each other.

Summary of the invention The present invention resides, basically, in anelectrical distribution system which comprises regulated polyphasealternating current mains and wound rotor induction motors, i.e., motorshaving slip-ring rotors, energized from the alternating current mains,these motors giving off their rotary energy, via direct current pulseconverter means, to direct current mains. Load means are connected tothe direct current mains. The wound rotor induction motors which areconnected between the alternating current mains and the direct currentmains are so ted States Patent O 'ice controlled that the average powersupplied to the direct current mains from the rotor means is equal tothe power drawn by the direct current load means. The invention furthercomprises a full-wave rectifier connected between the alternatingcurrent mains and the direct current mains, a switchable ballastresistor connected across the direct current mains, and means forelectronically switching the ballast resistor to and from the directcurrent mains so that if excess power is fed to the direct currentmains, the same is dissipated by the ballast resistor, while if there isan excess of power drawn from the direct current mains, the rectifiersupplies the additional power.

Brief description of the drawings FIGURE 1 is a block diagram of oneillustrative embodiment of the invention.

FIGURE 2 is a schematic diagram of several of the circuits disclosed inblock form in FIGURE 1.

FIGURE 3 is a schematic diagram of several of the circuits disclosed inblock form in -FIGURE 2.

Description of the preferred embodiments Referring now to the drawings,FIGURE 1 shows polyphase alternating current mains 1 which areconnected, via a control circuit 2 incorporating reversing and brakingthyristors, to an asynchronous electric motor 3. The rotor energy of themotor 3 is taken off by means of slip rings and, via an uncontrolledrotor rectifier 4 and a pulse converter 5 and is applied to directcurrent mains 6.

In a practical embodiment, a plurality of such arrangements 3, 4, 5, asdescribed above, will be connected between the alternating current mainsand the direct current mains. The direct current mains can, for example,draw the major portion of their energy from the alternating currentmains 1 via a transformer 7 and a full-wave rectifier 8. If desired, afull-wave inverter 9 can be connected in parallel with the rectifier y8if direct current energy is to be fed back into the alternating currentmains. A capacitor 10` is connected across the direct current mains.

One load connected solely to the direct current mains is shown as beinga direct current motor 11, together with its starter or control circuit12. Another direct current load is shown as being a short-circuit rotormotor 13 which has its energy supplied to it via a pulse inverter 14.

In order to increase the reliability of the system, an auxiliary load orballast resistor 16 is connected across the direct current mains 6 viaan electronic switching circuit 17, which automatically switches ballastresistor 16 into the circuit when the D.C. voltage between conductors 6exceeds a predetermined voltage.

Also shown are two single-phase pulse converters 18 -and 19 which areenergized by the direct current mains. The pulse converter 18 isconnected across the armature of a direct current motor 21, while thepulse converter 19 is connected across the shunt field winding 20 of themotor. The circuitry 18, 19, 20, 21, can be used to replace aWard-Leonard set, this being done by using quiescent electronicinverters, As a result, the efiiciency of the system is increased ascompared to conventional Ward- Leonard converters.

It will be seen from the above, that, according to the presentinvention, the electrical distribution system comprises both alternatingcurrent mains of constant voltage as well as direct current mains ofconstant voltage. The wound rotor induction motor means, of which onlyone example 3 is shown, have a stator which is energized from thealternating current mains, while the rotors apply their rotor energy,via respective direct current pulse converter means 5, to the directcurrent mains. The load means are connected to the direct current mains.The wound rotor induction motor means are so controlled that the averagepower supplied to the direct current mains from the rotors of the motorsis approximately equal to the power drawn by the direct current loadmeans. The full-wave rectifier 8 also applies direct current energy fromthe alternating current mains to the direct current mains. The resistor16 is connected to the direct current mains, while the electronicswitching means 17 serves for switching ballast resistor 16 to and fromthe direct current mains so that if an excess of power is fed to thedirect current mains, the same is dissipated by the ballast resistor,while if there is an excess of power drawn from the direct currentmains, the rectifier 8 supplies the additional power.

Thus, the present invention is based on feeding a plurality of loadsfrom the alternating .and direct current mains. The arrangement is suchthat the alternating current mains have asynchronous motors connected tothem which, in a cascade circuit, feed a portion of the alternatingcurrent energy into the direct current mains, the latter energizing somany loads that the power taken from the direct current mains is equalto or greater than the power applied thereto via the asynchronousmotors. The loads connected to the direct current mains are primarilydirect current motors or asynchronous motors which are fed viaself-controlled inverters.

The above-described ballast resistor circuit is provided in order toincrease the reliability of the system as a whole. The electronicswitching circuit 17 operates to switch in the ballast load resistorwhen the electrical energy fiowing into the direct current mains via theasynchronous motors is greater than the instantaneous power drawn by theloads connected to the direct current mains.

In practice, the purpose of the capacitor connected across the directcurrent mains 6 is provided in order to filter out ripple and currentpulses.

FIGURES 2 and 3 show portions of the above-described embodiment ingreater detail. Referring to FIG- URE 2, the polyphase (three-phase)line 1 is connected to asynchronous motor 3. The energy is taken off therotor 3 via slip rings and fed to the D.C. net via an uncontrolledrotary rectifier 4 with the aid of the conventional pulse transformer 5.

The pulse transformer 5, shown Within the phantom lines, incorporates agatable semiconductor rectifier element 6', which periodicallyshort-circuits the output of the rectifier 4 or which feeds therectifier output into the D.C. net 6 via the diode 9' and the line 11.The element 6' is positively commutated by means of the turn-off circuitwhich incorporates the turn-off capacitor 12', a resonant circuitcomprising the diode 13' and the choke 14', as well as the turn-offthyristor 15 which, upon firing, releases the energy stored in thecapacitor for interrupting the current flow in the controllablesemiconductor element 6. For controlling these two rectifiers, the rotorcurrent of the asynchronous motor 3 is reproduced in the load by meansof a D C. transformer 15" of a rectifier bridge 17 and is compared atthe input of the trigger 19' with a nominal current I now derived from apotentiometer 20.

The outputs of the trigger 19' are applied to the firing circuits V1, V2and, via transformer U2, U1, serve as output values for producing thefiring voltages for the semiconductor elements 6', 15', respectively.

The details of the resonant circuits V1, V2 are shown in FIGURE 3.

The ballast resistor 16 has asociated with it the controlledsemiconductor element 17a, and the commutating circuit consisting of thecommutating capacitor 12a, the resonant circuit comprising elements 13a,14a, and the turn-off thyristor 15a. The pulses controlling the resistor16 are `applied via the transformers U1, U2, the same being connected toresonant circuits V1, V2 and a trigger Tr. The inputs to the trigger, Eand O, are taken directly from the D.C. bus bars, and they produce thefollowing operation: if the voltage across the rotor of the asynchronousmotor 3 is too large, that is to say, if the voltage exceeds a nominalvalue equal to the response threshold of the trigger, the ballastresistor 16 is connected in parallel with the D.C. net. This will occurwhenever the power output coming from the asynchronous motor 3 isgreater than the power drawn by the D.C. load connected to the D.C. net.Since the semiconductor rectifier is an electronic switch capable ofoperating nearly at the speed of light, it can bridge power peaks.

The operation of the turn-off circuits for the rectifiers 6' and 17a isdescribed in GE Manual 1962, 2nd edition, the D.C. converter beingdescribed in AEG-Mitteilungen, 1959, pages 606 to 609.

The particular advantage of the present invention is that the cascadeallows the asynchronous machines to operate very simply and in a stablemanner in all four quadrants of the speed-torque graph. This requiresdirect current mains which can readily operate in conjunction withalternating current mains.

By virtue of the fact that the direct current mains are energized fromthe alternating current mains via a rectifier, there is obtained theadditional advantage that the rectifier need not be designed to supplythe power which is continuously drawn by the loads connected to thedirect current mains, inasmuch as part of the energy for the directcurrent mains comes directly from the alternating current mains via theasynchronous machines.

Finally, the present invention has been found to operate at a higherefficiency than heretofore known conventional semiconductor controlcircuits. The circuit is not limited by the characteristics of a currentcontrolled inverter; there are no circulating currents; and the circuitas a whole uses less expensive rectifying means.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes, andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim:

1. An electric energy distribution system comprising, in combination:

(a) means forming alternating current mains of constant voltage;

(b) means forming direct current mains of constant voltage;

(c) wound rotor `induction motor means connected to said alternatingcurrent mains for drawing energy therefrom, said motor means havingrotor means;

(d) means interconnecting said rotor means of said motor means and saiddirect current mains to enable the rotor energy to be applied to saiddirect current mains;

(e) load means connected to said direct current mains;

(f) said motor means being distributed between said alternating anddirect current mains such that the average power supplied to said directcurrent mains from said rotor means is equal to the power drawn by saidload means;

(g) rectifier means for energizing said direct current mains from saidalternating current mains;

(h) resistance means; and

(i) electronic switching means for rapidly switching said resistance toand from said direct current mains such that if there is an excess ofpower fed to said direct current mains, the same is drawn by saidresistor means while if there is an excess of power drawn by said directcurrent mains, said rectifier means supplies the additional power.

2. The combination deiined in claim 1 wherein said rectifier meanscomprise a full-wave rectifier.

3. The combination dened in claim lgwherein said means (d) comprisedirect current pulse converter means.

4. The combination defined in claim 1 wherein said load means include acage rotor motor which is connected to said direct current mains viainverter means.

5. The combination defined in claim 1 wherein said load means include ashort-circuit rotor motor which is connected to said direct currentmains via self-controlled pulse inverter means.

6. The combination delined in claim 1 wherein said load means include adirect current motor having an armature and a shunt field, a first pulseconverter connected across said direct current mains and to saidarmature, and a second pulse converter connected across said directcurrent mains and to said shunt.

7. The combination dened in claim 1 wherein said direct current mainsinclude two lines and a capacitor connected across said two lines.

8. The combination defined in claim 1, further comprising a full-waveinverter connected between said alternating and direct current mains forfeeding energy back from said direct current mains to said alternatingcurrent mains.

9. An electric energy supplying system which comprises: polyphasealternating current mains of constant voltage; direct current mains ofconstant voltage; wound rotor induction motor means energized from saidalternating current mains, said motor means having rotor means whichgive off their rotor energy, via direct current pulse converter means,to said direct current mains; load means connected to said directcurrent mains; said wound rotor induction motor means being sodistributed between said two current mains that the average powersupplied to said direct current mains from said rotor means is equal tothe power of the direct current load means; a full-wave rectifierconnected between said two current mains for feeding said direct currentmains from said alternating current mains; resistance means connected tosaid direct current mains; and means for switching said resistance meanselectronically quickly to and from said direct current mains, theswitching in and out of said resistance means being so regulated that ifthere is an excess of power fed to the direct current mains, the same isdrawn by said resistance means, while if there is an excess of powerdrawn by said direct current mains, said rectifier supplies theadditional power.

References Cited UNITED STATES PATENTS 1,915,074 6/ 1933 Stone 307-26 X3,136,937 6/1964 Miljanic 318-197 3,227,937 1/ 1966 Koppelmann et al.318-237 3,329,877 7/1967 Shibata 318-197 X ORIS L. RADER, PrimaryExaminer ALFRED G. COLLINS, Assistant Examiner U.S. Cl. X.R. 307-26, 82

